This invention relates to a steering clutch and brake control for track-type vehicles.
In the conventional steering system having multiple disc wet type clutches and brakes both of which can be engaged by the force of the spring and disengaged by fluid pressure overcoming the force of the spring, a fluid pressure gradually increasing valve is required for each of the clutches whilst a fluid pressure gradually reducing valve is required for each of the brakes in order to use the clutches and brakes, respectively, under half clutch condition and half brake condition. In order to actuate such clutches and brakes on both sides of the vehicle, it is required to use four independent spools to increase and reduce the fluid pressure gradually.
In the fluid system disclosed in U.S. Pat. No. 3,895,703 wherein the clutch fluid pressure and brake fluid pressure are independently controlled by a single spool valve, the arrangement is made such that, with actuation of the spool, the clutch fluid pressure is first increased gradually and then the brake pressure is increased gradually, and so it is not suitable for controlling the above-mentioned steering system.